That only worked because the traffic to bandwidth cost ratio was small.
Youtube would cost any normal company untold millions per month just in bandwidth costs alone, and there's actually so much more to it. I would bet money that even Discord's bandwidth bills are at least 1 million USD per month if not more.
Don't want to spend an arm and a leg for bandwidth? Don't include megabutts of JS, CSS, images, etc. Optimize and respect your users/guests.